15. Table 10 10 lists the mean salary, in thousands of dollars, of full-time instructional faculty on nine-month contracts in United States institutions of higher education in 1993-1994, by gender and i ank.

a) Suppose that gender is the explanatory variable. Identify the response variable and the control variable.

b) Describe the bivariate relationship between gender and salary.

c) Describe the relationship between gender and salary, controlling for academic rank.

d) A hypothesis of interest for these vanables is "Controlling for academic rank, annual salary and gender are independent" Draw a causal diagram that is consistent with this hypothesis. Refer to your interpretation in part (c). and comment on whether the hypoth- csis in fact seems plausible.

e) The overall difference of 9.5 thousand dollars between mean income of men and women is larger than the difference for each academic rank. Explain how this could be TABLE 10.10 Academic Rank Gender Professor Associate Assistant Instructor Overall Men 619 46.2 388 29.8 49.6 Women 54 7 43.2 362 281 401 Sure US. Department of Education National Center for Education Statistics, Digest of Education Statistics. 1995, p 240